Origin of the stellar Initial Mass Function (IMF) in the W43-MM1 ridge

Transcription

1 Origin of the stellar Initial Mass Function (IMF) in the W43-MM1 ridge Fabien Louvet (Universidad de Chile & IPAG Grenoble) Special credits to: F. Motte, T. Nony, S. Bontemps, A. Gusdorf, P. Didelon, P. Hennebelle, Q. Nguyen Luong, N. Peretto, N. Schneider, T. Csengeri, A. Zavagno, and the Herschel/HOBYS and W43-HERO consortia. November 29th, 2017 F. Louvet, East-Asia ALMA workshop 1/12

2 Formation of massive clusters and high-mass stars Open questions: Where do high-mass stars and massive clusters form? Thresholds for (high-mass) star formation? cf. Kelsey s talk: what kind of physical conditions give birth to what kind of stars? Is stellar feedback essential to define the final mass of massive stars? How is the IMF in massive clusters? What can we make to start answering? Outline morphological differences between high-mass star forming regions and low-mass star forming regions. Study of the relation between cloud features and star-formation. F. Louvet, East-Asia ALMA workshop 2/12

3 Different cloud structures form low- & high-mass stars Disorganized network of filaments versus single dominating filamentary clouds N H2 map of Vela D Hill et al N H2 map of the DR21 ridge Hennemann et al low-mass protostars high-mass protostars F. Louvet, East-Asia ALMA workshop 3/12

4 Low-velocity shocks in/on Ridges and Hubs Large scale SiO emission in high-mass star forming regions: e.g G W43 G e.g. Jimenez-Serra+2010; Nguyen Luong+2011, 2013; Sanhueza+2013 SiO is mostly known to trace high-velocity shocks Nguyen-Luong+2013 Louvet et al F. Louvet, East-Asia ALMA workshop Interferometry? 4/12 4

5 Low-velocity shocks in/on Ridges and Hubs LVC HVC Very homogeneous LVC emission! ~6km/s width Vlsr from 95 km/s to 98 km/s >280 dedicated of shock models Best fit with low-velocity shocks (~8-12 km/s) & 10% of the SiO in the gas phase From Louvet et al F. Louvet, East-Asia ALMA workshop 5/12 5

6 Are thresholds and constant SFE correct in ridges? Lada et al. (2010, 2012) relation between SFR and cloud mass implicitly assumes a constant SFE in regions above the SF threshold (n H2 > cm -3 ). See also Evans et al. 2014, André et al. 2014, and SFR theoretical models. IRAM Plateau de Bure census of protostars in the W43-MM1 ridge - finds the most massive protostar: N1a: M 0.03 pc 1mm/3mm, Louvet et al pc - investigates SFE within subregions A, B, C, D of different density F. Louvet, East-Asia ALMA workshop 6/12

7 Are thresholds and constant SFE correct? SFE measured within the W43-MM1 ridge and in numerical simulations increases with n H2 (Louvet et al. 2014). In contradiction with Lada s 2010/2012 prescription In agreement with previous CFE studies (e.g., Bontemps et al. 2010) Cloud density controls the SFE and the mass of the most massive stars that will form. SFE (%) W43-MM1 ridge and numerical simulations vs Lada s prescription n H2 (cm -3 ) Louvet et al See also Jorgensen+2007, Hatchell&Fuller+2008 F. Louvet, East-Asia ALMA workshop 7/12

8 The quest of the origin of the Initial Mass Function NIR Extinction and Herschel images of the Gould Belt clouds shows a good correspondance between the CMF and the stellar IMF (Alves et al. 2007; André et al. 2010; Könyves et al. 2010, 2015). From Könyves et al Studies limited to <5 M stars in regions not typical of the main mode of star formation in galactic disks. Well have a look at Hatchell & Fuller+2008 F. Louvet, East-Asia ALMA workshop 8/12

9 An ALMA view of the W43-MM1 mini-starburst protocluster Louvet et al. (2014) PdBI x 10 in resolution x 3 in sensitivity ALMA? Extraction of ~500 sources with the Getsources extraction tool (Men shchikov+2012) Reduced to ~280 sources after physical analysis 1.3 mm Scales (with ACA & TP) Μass completeness: ~ 1-3 M F. Louvet, East-Asia ALMA workshop 9/12

10 An ALMA view of the IMF origin in the mini-starburst protocluster of the W43-MM1 ridge ~300 pre- and proto-stellar cores of 2500 AU size. The M part of the CMF is much flatter than the IMF. Possible evolutions: - OB star feedback will steepen the final IMF - The high-mass cores will fragment (below 2500 AU) Motte, Nony, Louvet et al. subm to Nature - Core mass = available mass for accretion? - SFE increases with <n> The IMF will be atypical? See also Hatchell & Fuller+2008, Myers+2009b F. Louvet, East-Asia ALMA workshop 10/12

11 ALMA-IMF Large Programm PI: F. Motte (ESO) Co-PI: F. Louvet (Chile), A. Ginsburg (NRAO), P. Sanhueza (NAOJ) 15 Protoclusters Distance of 2-6 kpc Different stages F. Louvet, East-Asia ALMA workshop 11/12

12 The take away High-mass stars form in supermassive clouds We call those structures ridges or hubs (2-10 pc 3 with density > cm -3 ). They are hierarchical structure, dominating their environment. The star formation efficiency does correlate with the cloud volume density In opposition with the prediction of Lada (2010, 2012) there is no threshold in density above which the SFE would be constant (in W43-MM1). Formation of clouds, cores and stars is concomitant in HMSFR Origin of the initial mass function of stars (IMF)? Core mass function (CMF) of the W43-MM1 mini-starburst cluster is top-heavy. Will it evolve? By which means? The instantaneous IMF of a massive cluster may strongly depend on its pristine density & age? +kinematics, B field Please join the effort of the consortium of the ALMA-IMF Large Program! F. Louvet, East-Asia ALMA workshop 12/12